Conventionally, methods for detecting a defect in a circuit forming device such as a printed board with radiation or X-rays for example, include a method of detection from an image obtained by two-dimensional image processing on an X-ray transparent image in one direction of a circuit forming device, or a method of detection from an image obtained by two-dimensional image processing performed separately on X-ray transparent images in two directions and three directions.
In such detection methods, however, the inside of a circuit forming device can be viewed only in a two-dimensional manner. Thus a defect cannot be correctly located, a blind spot appears in some three-dimensional shapes of the circuit forming device, or inspections are difficult in some regions, so that accurate detection of a defect cannot be expected.
In order to address the problem, a method using X-ray tomosynthesis (hereinafter, referred to as X-ray CT) is proposed. In this method, a plurality of consecutive tomograms are generated, a defective region considered to be within the range of predetermined threshold values relative to each tomographic plane are binarized and detected, and the region is numbered, so that the position of a defect, the size of a cuboid circumscribing the defect, and so on are measured (For example, Japanese Patent Laid-Open No. 1-297772, page 5, FIG. 3).
In a device for inspecting a defective foreign matter using this method, consecutive tomogram data created by X-ray CT is binarized for each tomogram based on a predetermined threshold value and regions are numbered, so that the position of a defect, the size of a cuboid circumscribing the defect, and so on are measured.
However, in the conventional device for inspecting a defective foreign matter, a long defect such as a crack intersecting a tomographic plane at right angles is reduced in size on the display and thus becomes hard to extract, and processing on a large number of tomographic planes results in a longer inspection time.